Evaluation of Tsetse Salivary Gland Growth Factor-2 and Tsetse Antigen- 5 as Markers of Exposure to Tsetse Bites in Cattle

During their blood meals, arthropod vectors including tsetse flies inject saliva into their hosts to enhance their feeding efficiency. The salivary gland secretions include a number of proteins some of which can elicit the host’s immune response thereby being useful candidates for investigation as vaccine targets and/or markers of exposure to bites of these vectors which may aid disease control. This project evaluated the potential of tsetse salivary gland growth factor- 2 (TSGF-2) and tsetse antigen- 5 (Tag-5) as markers of exposure to tsetse bites in cattle. Both rTSGF-2 (810bp falling between 375 and 1094bp of the TSGF-2 cDNA) and rTag-5 (390bp falling between 78 and 468bp of the Tag-5 cDNA) gene fragments were expressed in BL21 DE3 E. coli expression host to obtain the respective recombinant proteins, rTSGF-2 and rTag-5. The rTSGF-2 was purified by Ni-NTA agarose column and, the two proteins were run on SDS and trans-blotted onto a nitrocellulose membrane, which was probed with pooled plasma from cattle of different tsetse exposure status. The ELISA tests were also run to show whether rTSGF-2 could be used to distinguish between tsetse exposed and non exposed cattle as well as trypanosome positive and negative cattle. Results revealed that rTSGF- 2 was expressed and purified in sufficient amounts of the expected size (31kDa) and it was recognized by plasma from tsetse exposed cattle. However, Western blotting and ELISA could neither distinguish between tsetse exposed from non exposed cattle (P˃0.05) nor trypanosome positive from negative cattle (P˃0.05). This would indicate possible cross reactions with proteins from other vectors such as mosquitoes and ticks to which the control animals could as well have been exposed. The rTag- 5 was expressed in very low quantities which hindered its purification making some of the subsequent tests impossible. It was also recognized by plasma from the different groups of cattle as above. Therefore, both rTSGF-2 and rTag-5 are recognized by cattle plasma antibodies but they are not reliable as markers of exposure specific to tsetse bites and cannot specifically determine trypanosome infection status in cattle. Similar proteins secreted by other vectors should be evaluated for recognition by antibodies produced against rTSGF-2 and rTag-5 to check for possible cross reaction, and future studies should be based on proteins expressed from gene regions unique to Glossina to limit such cross reactions.